1. Field of the Invention
The present invention relates to an image forming apparatus such as a printer, a facsimile, and a copy machine.
2. Description of the Related Art
In connection with an image forming apparatus, it is known that units such as a writing unit, a fixing unit, and a developing unit that are disposed in an image forming unit within the apparatus generate heat and increase the internal temperature of the apparatus.
For example, in the developing unit, when a developer stirring and conveying member for stirring and conveying a developer inside the developing unit is driven, frictional heat generated by sliding friction between the developer stirring and conveying member and the developer, or between the developers increases the internal temperature of the apparatus. Frictional heat generated by sliding friction between a developer and a developer regulating member for regulating the layer thickness of the developer carried on a developer carrier before the developer is conveyed to a developing area also increases the internal temperature of the apparatus. Furthermore, when the developer regulating member regulates the thickness of the developer, frictional heat generated by sliding friction between developers increases the internal temperature of the apparatus.
An increase in temperature may cause the toner to melt and be fixed onto the developer regulating member, the developer carrier, the image carrier, or the like, so an image with a stripe-like abnormal defect may be produced. Further, even though the toner is not melted, the toner having an increased temperature gets stressed from pressure or friction. Thus, there may be a problem in that an external additive on the toner surface comes to be buried into the inside of toner or be separated from the surface, which causes the toner component to stick to the carrier surface. This problem may lead to a lack of stability in developing capability in the long term. Particularly, in the case of using the toner having the low melting temperature to reduce fixing energy, an abnormal image may be easily generated due to fixing of the toner.
For this reason, there has been known an image forming apparatus in which external air is introduced into the apparatus by an air-cooling fan and is conveyed to the periphery of the developing unit through a duct to air-cool the developing unit and thereby to prevent an excessive increase in temperature. However, as the size of the image forming apparatus decreases, the density inside the apparatus increases and a space around the developing unit also decreases. Therefore, it becomes more difficult to reserve a space for the duct for conveying the air current from the air-cooling fan to the periphery of the developing unit. Therefore, it becomes difficult to forcedly air-cool the developing unit.
Japanese Patent Application Laid-open No. 2006-003628 discloses an image forming apparatus using a liquid cooling system in which a developing unit is cooled by circulation of a liquid. A liquid cooling apparatus includes: a heat receiving unit; a heat radiating means for radiating the heat of the cooling liquid; a tube disposed to allow the cooling liquid to circulate through the heat receiving unit and the heat radiating means; and a conveying means for conveying the cooling liquid inside the tube. The heat receiving unit is in close contact with the wall surface of the developing unit that is a temperature increasing portion to receive heat from the developing unit by a cooling liquid therein. The liquid cooling apparatus can perform cooling more effectively than the air cooling apparatus and thus effectively cool the developing unit. Further, since the tube for circulating the cooling liquid has a smaller cross section than the duct, even if the space around the developing unit is cramped, the tube can be disposed around the developing unit. Thus, even if the component density inside the apparatus increases, the developing unit may be cooled down.
However, if the cooling liquid conveyed inside the tube by the conveying means pulsates, the pulsation of the cooling liquid causes the heat receiving unit to vibrate, and the vibration is transferred to the image forming unit via the developing unit. This has a bad influence on an image forming operation, so that a good image cannot be formed.
The writing unit and the fixing unit disposed in the imaging unit as the temperature increasing portions have the same problem as described above.
According to the present invention, since the cooling liquid flows from the conveying unit to the heat receiving unit via the radiator, the pulsation generated in the cooling liquid is attenuated by the conveying unit while the cooling liquid flows through the complicated flow passage in the radiator before the cooling liquid is sent to the heat receiving unit. This reduces the vibration that is generated in the heat receiving unit due to the pulsation of the cooling liquid. The vibration to be transferred to the image forming unit via the temperature increasing portion is reduced. Accordingly, it is possible to prevent the phenomenon that good image formation cannot be performed since the vibration has a bad influence on the image forming operation.